(1) Field of the Invention
The present invention relates to an improvement in a buckle for a seat belt system provided to protect an occupant in a vehicle seat in the event of a collision. The buckle is assembled in the seat belt system, so that the buckle receives therein an associated tongue plate in a latched state when the seat belt system is used. The above improvement has made it possible to prevent the production of unpleasant noise which otherwise tends to occur due to rattling of the tongue plate upon its latching on the buckle.
(2) Description of the Related Art
To protect an occupant in the event of a collision or a similar accident, a vehicle seat is provided with a seat belt system such as that illustrated in FIG. 5.
Upon use of such a seat belt system, a tongue plate 2 to which a webbing 1 is fastened is latched on a buckle 4 connected to a flexible wire 3 to restrain an unillustrated occupant by the webbing 1. Accordingly, the occupant in a seat 5 is prevented from being thrown forward even in the event of a collision. Upon egress, the occupant presses a buckle button of the buckle 4 to release the latching between the tongue plate 2 and the buckle 4 so that the webbing 1 no longer prevents the occupant from leaving the seat 5.
To date, a variety of constructions have been used to provide such buckles. However, the basic structure is composed, as shown in FIG. 6 by way of example, of a buckle base 6 made of a metal plate, a buckle button 7 movable in parallel with the length of the buckle base 6 to move a buckle latch piece (not shown in FIG. 6) and hence to release the latching between the buckle 4 and tongue plate 2, and a two-piece cover 8 substantially enclosing the buckle button 7 and buckle base 6.
The cover 8 defines an opening 9 through which a portion of the buckle button 7 is selectively movable back and forth. In the opening 9, a clearance 10 having a width greater than the thickness of a proximal end portion of the tongue plate 2 is defined between the upper surface of an outer end portion of the buckle base 6 and the buckle button 7 so that the proximal end portion of the tongue plate 2 may be inserted into the buckle 4.
Provided between the cover 8 or a support 11, said support being fixed relative to the buckle base 6, and an inner side wall 12 of the buckle button 7 is a compression spring as a button spring 13, whereby an outward spring force is exerted against the buckle button 7.
To latch the tongue plate 2 on the buckle 4 constructed as described above, insertion of the proximal end portion of the tongue plate 2 into the clearance 10 causes an unillustrated buckle latch piece, which is supported on the buckle base 6, to automatically advance into a slot 14 formed in the vicinity of the proximal end of the tongue plate 2 under the spring force of a spring (not shown either), so that the buckle latch piece prevents separation of the buckle 4 and tongue plate 2 from each other.
To release the latching between the buckle 4 and the tongue plate 2 upon egress, it is simply necessary to press the buckle button 7 of the buckle 4 against the spring force of the button spring 13. As a result, the buckle latch piece is caused to retreat from the slot 14 of the tongue plate 2 to render the tongue plate 2 ready to be withdrawn from the inside of the buckle 4. In practice, the tongue plate 2 is ejected out from the buckle 4 by means of a ejector spring.
Conventional buckles for seat belt systems, which have been constructed as described above, are however accompanied by the inconvenience set out next.
The width W of the clearance 10 defined between the buckle base 6 and the buckle button 7, more precisely, between the lower edge of the opening 9 formed in the cover 8 and the lower surface of the buckle button 7 as shown in the drawing has to be greater than the thickness T of the tongue plate 2 to ensure easy insertion of the tongue plate 2 into the buckle 4 (W&gt;T). The above definition for the clearance 10 will apply equally to all clearances to be referred to hereinafter.
However, when the width W of the clearance 10 is designed greater than the thickness T of the tongue plate 2 as mentioned above, the tongue plate 2 tends to rattle inside the buckle 4 upon latching of the tongue plate 2 on the buckle 4. The tongue plate 4 and buckle base 6 are both made of metal. The noise caused by hitting of the tongue plate 2 and buckle base 6 against each other may therefore be unpleasant to the occupant.
With a view toward solving such an inconvenience, DE 31 28 139 C2 published Aug. 18, 1983 proposes to cover the tongue plate 2 with a synthetic resin so that even when the tongue plate 2 rattles inside the buckle 4 no intermetal hitting would take place, thus avoiding any unpleasant noise.
Covering of the tongue plate 2 with a synthetic resin as proposed in the German patent publication however inevitably leads to a substantially higher manufacturing cost although noise production may be prevented to a certain extent.
On the other hand, U.S. Pat. Nos. 4,577,378 and 4,597,141 issued Mar. 25 and July 1, 1986 respectively propose to form at a part of the cover 8 a resilient portion which extends into the opening 9. The resilient portion serves to suppress the tongue plate 2 inserted into the buckle 4, whereby the tongue plate 2 may be prevented from rattling inside the buckle 4.
The integral formation of the resilient portion with the cover 8 made of a synthetic resin however results in a higher cost for the fabrication of a mold therefor. This increases the manufacturing cost of the buckle 4. In addition, the resilient portion has the potential problem that it could be damaged while the tongue plate 2 is repeatedly inserted into and withdrawn from the buckle 4. Damage of the resilient portion then leads to the problem that the resilient portion is no longer effective for the prevention of noise.